Well screens are typically used to exclude sand and formation fines from fluids produced from subterranean wells. One or more sand control screen assemblies are commonly included in the completion string to control the movement of formation particles. Sand control screen assemblies are commonly constructed by installing one or more screen jackets on a perforated base pipe or liner. The screen jackets may include one or more drainage layers, one or more screen or filter layers, such as wire wrapped screen or single or multilayer wire mesh screen, and a perforated outer shroud.
Filter layers are known in the art and can be of various construction. For example, in “wire-wrapped” screen structures, the filter is formed by wrapping wire around the base pipe, with rods providing a standoff between the wire and the base pipe. Mesh screens consist of a woven single- or multi-layer mesh, typically of steel or other metal, shaped and combined with a protective, perforated outer covering in a cartridge, or jacket, which is slipped over a perforated base pipe. Filter layers can be formed of sintered or unsintered metal, bonded or non-bonded metal, wire mesh, multilayer wire mesh, woven wire, woven mesh, diffusion-bonded mesh, etc., as are known in the art or become known in the art. Multiple filter layers or laminates can be used in conjunction. As used herein, the term “filter layer” and similar includes multi-layer filters unless indicated otherwise.
Typically, a layer placed behind (radially inward from) the filter layer is provided to reduce resistance to fluid flow through the filter layer and is referred to as a “drainage layer.” In some screen assemblies, the drainage layer is provided by placing a coarse mesh grid behind (radially inward of) the fine mesh filter layer. The drainage layer may also be made of a perforated stainless steel tube or liner, and can be referred to as an inner shroud since it is similar in construction to an outer shroud. A drainage layer can also be formed by creating a stand-off between the filter layer and inner shroud, such as by providing longitudinally and/or radially extending ribs, splines, etc., to maintain spacing between the layers.
An outer layer is typically referred to as a shroud or sleeve and can be formed of a metal tubular member having perforations extending radially through the tubular wall. The outer shroud is primarily for protection of the filter layer during insertion into the wellbore, handling, transport, etc., and can provide structural support as well. In some screen assemblies it is known to provide a stand-off between the outer shroud and the filter layer such as by providing ribs, splines, dimples, etc., on the interior surface of the outer shroud or outer surface of the filter layer.
It is known in the art to form the outer shroud separately from the filter body and slide it over an end of the inner tubular member until it surrounds the filter layer. After the shroud is disposed around the filter layer, the shroud is plastically deformed radially inwardly to reduce the inner diameter of the shroud to a value such that the filter layer can expand against the shroud. This process is also known as “swaging,” and is typically achieved using a reducing mill or die. Swaging is undesirable because it adds to the time and expense of manufacturing the filter, deforms the outer shroud putting additional stresses on the shroud and affecting its material makeup, and does not guarantee that the clearance between the filter body and the shroud has been properly eliminated.
Where wire mesh is used as a filter layer in a well screen, it has been found that bonding operations (such as welding and brazing) performed on the wire mesh are detrimental to the long-term usefulness of the wire mesh. For example, the wire mesh may be thus made more susceptible to corrosion. An attempt has been made to address the problems associated with a bonded wire mesh filter layer by swaging an entire screen jacket, including the filter layer, onto a base pipe. An overlap in a wrap of the wire mesh filter layer is used instead of welding to seal the filter layer against sand migration. However, this method of swaging the screen jacket also imparts undesirable stress concentrations in the filter layer.
Assembly methods have been developed for assembling the various layers of a screen jacket or assembly. The layers can be formed by wrapping or spiral wrapping successive layers. For example, a metal wire is wrapped about an inner shroud to form a drainage layer, a filter layer is wrapped over the drainage layer, and an outer shroud is wrapped over the assembly. Wrapping techniques typically require welding, brazing, or other method, of creating a seam where the wrapped material meets, such as at the longitudinal ends of the filter layer, to form a cylinder. Obviously, such welding or other method can damage the filter layer and compromise the effectiveness and life of the screen assembly. Further, the filter layer longitudinal edges can be overlapped and secured by welding, brazing or other method involving heating of metal, crimping or other plastic deformation, or by friction with the inner and outer shrouds.
Alternately, the layers of the screen assembly can be positioned by moving (typically, lowering) one tubular layer over or into another tubular layer. For example, the outer shroud can be lowered onto a prepared inner shroud and filter layer. Such an operation requires a clearance or “play” between the layers.
It is desirable to have a tight-fit and radially thin screen assembly. Consequently, it is typical in the art to perform a secondary manufacturing process on the assembled screen assembly. Secondary processes include radial expansion, radial reduction, swaging, etc., to reduce or eliminate layer clearances, provide a press-fit or tight-fit assembly, “sandwich” the filter layer between shroud layers, etc. For example, the outer shroud can be radially reduced into secure contact with the filter layer. Alternately, the inner shroud and filter layer can be radially expanded within the outer shroud.
Further disclosure regarding screen assemblies and their manufacture can be found in the following references, each of which are hereby incorporated herein for all purposes: U.S. Pat. No. 7,287,684, to Blackburne, Jr., issued Oct. 30, 2007; U.S. Pat. App. Pub. No. 2007/0114171, to Chen, published May 24, 2007; U.S. Pat. No. 7,578,344, to Hopkins, issued Aug. 25, 2009; U.S. Pat. No. 8,176,634, to Bonner, issued May 15, 2012.
Therefore, it will be appreciated that improvements would be desirable in the art of constructing well screens. These improvements may find use in well screens which either do or do not have wire mesh filter layers.